Investigation of the effects of thermal annealing on the structural, morphological and optical properties of nanostructured Mn doped ZnO thin films

The control of the optical properties of ZnO nanostructured thin films by using different dopant elements paves the way for the development of potential materials for photonic and optoelectronic applications. In this work manganese (Mn) doped ZnO thin films were fabricated by rapid thermal evaporation method on a glass substrate having the same Mn content level of ~10% and annealed at different temperatures. XRD analysis showed that the annealed layers have hexagonal wurtzite structure, however, the unannealed layers showed only Zn peaks without any preferential direction. The elemental analysis of the films has been investigated by XPS, which revealed the presence of Mn and oxygen atoms for all layers. In addition, it was observed by FIB-SEM that the morphology of thin films changed with the annealing temperature. For an anneal at 500 °C nanoneedles appeared. Raman spectroscopy showed E1 (TO) mode in the sample annealed at 500 °C which was attributed with the formation of nanoneedles structures. The optical transmission of the annealed films was in the range of 75–77% and the optical bandgap varied from 3.97 to 3.72 eV. These variations are related to the structural and morphological changes of the thin films with annealing temperature. •The effect of thermal annealing on the physical properties of nanostructured Mn doped ZnO thin films was investigated.•XRD analysis revealed that MZO layers after annealing crystallize in hexagonal wurtzite phase.•The morphology of MZO films changed with the annealing temperature. For an anneal at 500 °C nanoneedles appeared.•Raman measurements have also shown an additional mode E1 (TO) at 467 cm−1 associated with the apparition of nanoneedles.•The optical constants n, α and the thickness d were successfully identified and determined only from the transmittance spectra using the PSO algorithm.